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Disease Note. First Report of Resistance of Helminthosporium solani to Thiabendazole in the United States. C. L. Merida, Department of Plant Pathology, Cornell University, Ithaca 14853. R. Loria, Department of Plant Pathology, Cornell University, Ithaca 14853. Plant Dis. 74:614. Accepted for publication 8 May 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0614A. Silver scurf of potato (Solanum tuberosum L.), caused by Helminthosporium solani Dur. & Mont., appears to be increasing in the
northeastern United States. We suspected the increase could associated with resistance of H. solani to thiabendazole. This fungicide
is used for oontrol of other diseases of potato tubers, and H. solani
isolates with resistance to thiabendazole have been documented in
the United Kingdom (1). Although silver scurf has generally not been
a target for thiabendazole applications, this fungicide is effective
against H. solani and docs control this disease on potato tubers in
storage. H. solani was isolated from tubers with silver scurf collected
from five locations in New York State. Eight single-spore isolates
were grown on V-8 agar amended with 1, 3.2, 10, 31.6, or 100 mg/
L of thiabendazole, and radial growth was measured after 20 and
40 days at 21 C. Two of the eight isolates tested were resistant to
the fungicide. Sensitive isolates did not grow at concentrations greater
than 1 mg/L of thiabendazole. Resistant isolates grew at concentrations
up to 31.2 mg/L of thiabendazole. The increase in silver scurf on
potatoes in the northeastern United States may be due to the selection
of thiabendazole·resistant isolates of H. solani. |